Benzocyclobutene (BCB) or benzocyclobutadiene is the simplest polycyclic aromatic hydrocarbon, being composed of a benzene ring fused to a cyclobutene ring. It has chemical formula C8H6 and CAS number [ ]. It is antiaromatic, because it has 4n pi electrons. For this reason the compound is very reactive. It will easily dimerize or polymerize and reacts as the dienophile in Diels-Alder reactions 
BCB is frequently used to create photosensitive polymers. BCB-based polymer dielectrics may be spun on or applied to various substrates for use in Micro Electro-Mechanical Systems (MEMS) and microelectronics processing. Applications include wafer bonding, optical interconnects, low-K dielectrics, or even intracortical neural implants.
- Carey, Francis A.; Sundberg, Richard J.; (1984). Advanced Organic Chemistry Part A Structure and Mechanisms (2nd ed.). New York N.Y.: Plenum Press. ISBN 0-306-41198-9.